Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Bootstrap Zero - Open-source, free Bootstrap templates collection.
Telegram X - Meet Telegram X for iOS and Android – two new official apps that offer more speed, longer batter life and smooth animations.
Bootstrap Magic - Create your Bootstrap 4.0 themes easily with magic
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Material Design for Bootstrap 4 - Powerful and free UI KIT for the newest Bootstrap 4 and Material Design